It's late afternoon in west London and the Senegalese star Baaba Maal and Damon Albarn, from nearby in the neighbourhood, are lounging on a scrap of grass in the sun. Messing about on a bike beside them is east London rapper Kano, while tottering by on a pair of heels is Shingai Shoniwa from the band the Noisettes. She's another Londoner, although her mum comes from Zimbabwe.

There's one important question on Albarn's mind and it's nothing to do with what is, just now, his day job – although rehearsals for Blur's closing show for the Olympics are in full swing. "What I really need to know," he says in earnest, "is whether there's a proper bar on this train…"

On Sunday 2 September the train will pull out of Euston station with approximately 80 musicians on board, roughly half of whom comprise a who's who of African talent. As well as Baaba Maal, fresh from hosting his own Africa Utopia festival at the Southbank in London, there will be the blind husband-and-wife duo Amadou and Mariam from Mali; their compatriot, the kora player Toumani Diabaté; South African producer Spoek Mathambo; Ghanian rapper M.anifest; Egyptian rapper Karim Rush; Congo-born singer Baloji and dozens more. Wandering out of the photographer's studio now is another, Jupiter Bokondji, tired from playing a stunning show with his band Okwess International at the Womad festival in Wiltshire the previous afternoon. But peering into the sunlight, this rangy figure perks up. "Ah, Damon!" he begins, and they hug, before swiftly running out of words, his English being little better than the Englishman's French.

The pair first met on a trip Albarn made to the Democratic Republic of Congo in 2007 with the collective of musicians known as Africa Express. Conceived as a way of bringing western and African acts together, and run by an informal coterie of producers, promoters, managers and journalists, as well as Albarn himself, Africa Express played a surprise set at Glastonbury that year which proved the hit of the festival. Since then, there has been a further series of occasional shows, usually involving a cast of several dozen acts and lasting several hours: in London as part of the BBC's Electric Proms; in the middle of Paris; on a beach in northern Spain in front of a crowd of 40,000.

The western acts have included everyone from Franz Ferdinand to John Paul Jones, Led Zeppelin to Johnny Marr, Björk and members of the Yeah Yeah Yeahs. Those joining the enterprise next week will include Charli XCX, Rizzle Kicks and Jack Steadman from Bombay Bicycle Club, as well as Shingai Shoniwa and Kano.

"The purpose as I see it," says the rapper, between shots in the photo studio, "is to show Africa at its best, at its most creative."

According to the journalist Ian Birrell, one of Africa Express's co-founders: "There are so many stereotypes in the west about Africa, but we hope that by opening people's ears to the music they will then open their eyes a little to reality. After all, seven of the world's fastest-growing economies are African, and there is so much we can learn from there."

Then there's a stray figure who won't be on the train, isn't a musician, but who wants to show his support regardless. Suddenly, through the garden gate looms Rio Ferdinand, the Manchester United footballer. Introduced to Albarn through a mutual friend, the pair haven't simply become improbable table tennis partners. Rather, Ferdinand wants to see if his support can further spread the word about this venture.

"I wish I could be on the train," he says, "but it's too near the start of the football season. I'd only get in trouble."

The train will tour the UK for a week, with one big show each night before the circus rolls back into London for a final gig in the new Granary Square in King's Cross. Rehearsals will take place on board, in a baggage car salvaged from the old Orient Express. As far as the fabulous Malian singer Fatoumata Diawara, who's also here and will be on board, is concerned: "It will all be beautiful."

En route, the plan is also for a series of impromptu gigs in city squares and workplaces, for pop-up workshops and more. "Logistically," says Lauren Roth de Wolf, one of the organisers, "yes, it's going to be a nightmare."

Albarn interrupts: "Or if not a bar... I hope there'll at least be an old-fashioned tea trolley."

The Guardian is Africa Express's media partner. For more interviews with the artists involved and full coverage of life on board from 2 September, go to guardian.co.uk/music/africa-express

Africa Express is part of the London 2012 festival, a spectacular 12-week nationwide celebration running from 21 June until 9 September that brings together leading artists across the world with the very best from the UK